A thin film containing zinc has various characteristics such as optical characteristics, electrical characteristics, catalytic activity, and the like, and is used as a member in electronics parts and optical parts.
Methods for producing the above-mentioned thin film include flame deposition, sputtering, ion-plating, MOD processes such as coating thermal decomposition, sol-gel process and the like, chemical vapor deposition, and others. Chemical vapor deposition (hereinafter may be simply described as CVD) including ALD (Atomic Layer Deposition) is the most suitable production process owing to many advantages such as excellence in controllability of compositions and step coverage, suitability for large-scale production, capability of hybrid integration, and the like.
In the CVD processes, β-diketonate complexes excellent in stability and safety have been used as precursors supplying zinc to a thin film. For example, Patent Documents 1 to 3 reported methods for producing zinc-containing thin films using bis(pentane-2,4-dionato)zinc, and Non-patent Document 1 reported a method for producing zinc-containing thin films using bis(2,2,6,6-tetramethylheptane-3,5-dionato)zinc. However, since these complexes are solid, they are required to be either vaporized by sublimation or kept at high temperatures not lower than the melting points thereof in the step of vaporization of the raw materials, and there have been problems in supplying the raw material gas, such as insufficient amount of vaporization or temporal variation of vaporization, and problems in in-line raw material transport. Further, in the solution CVD process using a solution in which a solid precursor is dissolved in an organic solvent, the solid precursor is likely to precipitate due to variation of temperature, partial evaporation of the solvent or variation in concentration of the solution in the vaporization equipment, resulting in temporal variation of feed rate through clogging in feed lines or the like. Hence, there is a problem that it is impossible to produce a thin film with stable film-forming rate or stable thin film composition control.
In order to circumvent these problems, Patent Document 4 reported a method of using a liquid β-diketonate containing a mixture of two or more kinds of β-diketones. Due to use of a mixture, however, this method still has problems in stability of conditions in producing a thin film and solid precipitation.    Patent Document 1: Japanese Patent Application Publication No. H6-64738    Patent Document 2: Japanese Patent Laid-open Publication No. H8-3171    Patent Document 3: Japanese Patent Laid-open Publication No. 2003-236376    Patent Document 4: Pamphlet of WO98/46617    Non-patent Document 1: Microelectron. Eng., 29(14), 16972(1995)